I think the problem isnt that B&N offers this service (I've certainly bought used books before with no problems) but that they did not take responsibility for the problem.

Final score made a good suggestion - I suggest doing that. If they have no recollection or record of ordering the book for you, then they shouldn't have a problem with you fighting the charge.

But, this does not bode well for the company. I know eBay may sound more risky, but I have bought many books off eBay and if you have a problem, paypal will back you up as far as getting your money back.